diff --git a/lib/add-file-to-cache.js b/lib/add-file-to-cache.js
index 44040fd..f1b0a20 100644
--- a/lib/add-file-to-cache.js
+++ b/lib/add-file-to-cache.js
@@ -25,7 +25,7 @@ function getExtensionAndSampleRate(path) {
 }
 
 async function addFileToCache(client, logger, path,
-  {account_sid, vendor, language, voice, deploymentId, engine, model, text}) {
+  {account_sid, vendor, language, voice, deploymentId, engine, model, text, instructions}) {
   let key;
   logger = logger || noopLogger;
 
@@ -38,6 +38,7 @@ async function addFileToCache(client, logger, path,
       engine,
       model,
       text,
+      instructions
     });
     const [extension, sampleRate] = getExtensionAndSampleRate(path);
     const audioBuffer = await fs.readFile(path);
diff --git a/lib/purge-tts-cache.js b/lib/purge-tts-cache.js
index 86ba974..bafb5dd 100644
--- a/lib/purge-tts-cache.js
+++ b/lib/purge-tts-cache.js
@@ -12,7 +12,7 @@ const debug = require('debug')('jambonz:realtimedb-helpers');
  * @returns {object} result - {error, purgedCount}
  */
 async function purgeTtsCache(client, logger, {all, account_sid, vendor,
-  language, voice, deploymentId, engine, model, text} = {all: true}) {
+  language, voice, deploymentId, engine, model, text, instructions} = {all: true}) {
   logger = logger || noopLogger;
 
   let purgedCount = 0, error;
@@ -35,6 +35,7 @@ async function purgeTtsCache(client, logger, {all, account_sid, vendor,
         engine,
         model,
         text,
+        instructions
       });
       purgedCount = await client.del(key);
       if (purgedCount === 0) error = 'Specified item not found';
diff --git a/lib/synth-audio.js b/lib/synth-audio.js
index 4e72328..69159cc 100644
--- a/lib/synth-audio.js
+++ b/lib/synth-audio.js
@@ -171,7 +171,8 @@ async function synthAudio(client, createHash, retrieveHash, logger, stats, { acc
     engine,
     // model or model_id is used to identify the tts cache.
     model: model || credentials.model_id,
-    text
+    text,
+    instructions
   });
 
   debug(`synth key is ${key}`);
diff --git a/lib/utils.js b/lib/utils.js
index 81047b5..d973637 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -23,10 +23,11 @@ function makeSynthKey({
   voice,
   engine = '',
   model = '',
-  text
+  text,
+  instructions = '',
 }) {
   const hash = crypto.createHash('sha1');
-  hash.update(`${language}:${vendor}:${voice}:${engine}:${model}:${text}`);
+  hash.update(`${language}:${vendor}:${voice}:${engine}:${model}:${text}:${instructions}`);
   const hexHashKey = hash.digest('hex');
   const accountKey = account_sid ? `:${account_sid}` : '';
   const key = `tts${accountKey}:${hexHashKey}`;
diff --git a/test/synth.js b/test/synth.js
index 811639b..4ca2944 100644
--- a/test/synth.js
+++ b/test/synth.js
@@ -887,7 +887,8 @@ test('TTS Cache tests', async(t) => {
     // save some random tts keys to cache
     const minRecords = 8;
     for (const i in Array(minRecords).fill(0)) {
-      await client.set(makeSynthKey({vendor: i, language: i, voice: i, engine: i, model: i, text: i}), i);
+      await client.set(makeSynthKey({vendor: i, language: i, voice: i, engine: i, model: i, text: i,
+        instructions: i}), i);
     }
     const count = await getTtsSize();
     t.ok(count >= minRecords, 'getTtsSize worked.');
@@ -906,7 +907,7 @@ test('TTS Cache tests', async(t) => {
   try {
     // save some random tts keys to cache
     for (const i in Array(10).fill(0)) {
-      await client.set(makeSynthKey({vendor: i, language: i, voice: i, engine: i, text: i}), i);
+      await client.set(makeSynthKey({vendor: i, language: i, voice: i, engine: i, text: i, instructions: i}), i);
     }
     // save a specific key to tts cache
     const opts = {vendor: 'aws', language: 'en-US', voice: 'MALE', engine: 'Engine', text: 'Hello World!'};
@@ -944,10 +945,10 @@ test('TTS Cache tests', async(t) => {
     const account_sid = "12412512_cabc_5aff"
     const account_sid2 = "22412512_cabc_5aff"
     for (const i in Array(minRecords).fill(0)) {
-      await client.set(makeSynthKey({account_sid, vendor: i, language: i, voice: i, engine: i, text: i}), i);
+      await client.set(makeSynthKey({account_sid, vendor: i, language: i, voice: i, engine: i, text: i, instructions: i}), i);
     }
     for (const i in Array(minRecords).fill(0)) {
-      await client.set(makeSynthKey({account_sid: account_sid2, vendor: i, language: i, voice: i, engine: i, text: i}), i);
+      await client.set(makeSynthKey({account_sid: account_sid2, vendor: i, language: i, voice: i, engine: i, text: i, instructions: i}), i);
     }
     const {purgedCount} = await purgeTtsCache({account_sid});
     t.equal(purgedCount, minRecords, `successfully purged at least ${minRecords} tts records from cache for account_sid:${account_sid}`);